The availability of efficient and selective inhibitors of certain serine proteases would provide a new approach to the regulation of certain physiological functions (fertilization, blastocyst implantation, tissue remodeling) and the treatment of certain pathologies (emphysema, adult respiratory distress syndrome, glomerulonephritis, arthritis, inflammatory disorders, tumor invasion and metastasis). We have previously prepared halo enol lactones that appear to act, through a two-step acylation- alkylation sequence, as mechanism-based inactivators of the serine protease chymotrypsin. We are now planning to study the mechanistic details of the inactivation process, to determine what chemical species are involved and what residue is the site of alkylation; furthermore, we will utilize computer graphics- molecular modeling to rationalize relationships between inactivator structure and inactivating efficiency and potency, and to improve in the design of new inhibitors. Specific efforts will be made: (1) to prepare certain new lactones that will be used to investigate further an inactivation burst kinetic model, (2) to prepare lactones specifically labeled with C-13 as NMR spectroscopic probes to follow the chemical changes at specific atoms in the lactone during the sequence of steps leading to inactivation, (3) to develop enol lactone precursors of reactive Michael acceptors, (4) to develop inhibitors based on slow deacylation due to a predicted twisting of the acyl enzyme observed in certain beta-substituted lactones, and (5) to develop fluoroketones as transition state inhibitors of high potency. The compounds that demonstrate the best inhibitory properties towards chymotrypsin will also be prepared in forms that should make them suitable as inhibitor for elastase, trypsin, plasmin and plasminogen activator.